Termination of coaxial transmission lines



Dec. 20, 1960 w. D. PALMER EI'AL 2,965,858

TERMINATION OF COAXIAL TRANSMISSION LINES Filed June 4, 1957 INVENTORS.MLL/A/V D. l ll/YER A/Vfi JAC'UB EKUA JV E/IV Z2) J ,4

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United States Patent TERMINATION OF COAXIAL TRANSMISSION LINES WilliamD. Palmer and Jacob Bronstein, Baltimore, Md., assignors, by mesneassignments, to the United States of America as represented by theSecretary of the Air Force Filed June 4, 1957, Ser. No. 663,559

3 Claims. (Cl. 333-22) This invention relates in general to coaxialtransmission lines and particularly to an improved means for terminationthereof.

In the use of coaxial high frequency transmission line it is oftendesirable to provide a terminating impedance. This is particularly truewhen it is desired to connect external measuring apparatus to said linefor the purpose of ascertaining voltage, current or power output of thehigh frequency transmission system. Unless such a termination impedanceis of a value approaching the characteristic impedance of the line,readings on the measuring apparatus will be seriously affected due tothe impedance mismatch which causes reflection and standing waves alongthe transmission line. Impedance matching devices presently known to theart are not always available at low cost. Also many of these deviceshave undesirable reactance effects which aggravate the reflectionconditions referred to.

An object of this invention is to provide an inexpensive compact andsimple device for use as a terminating impedance for a coaxialtransmission line wherein the resistive component of said terminatingimpedance may be rapidly varied by the substitution of radio type carbonresistors of different resistive values.

Another object of this invention is to provide a novel coaxialtransmission line structure incorporating a termination impedance.

It is a further object of this invention to provide a terminationimpedance for a coaxial transmission line which will minimizereflections at higher frequencies.

These and other advantages, features and objects of the invention, willbecome more apparent from the following description taken in connectionwith the illustrative embodiment in the accompanying drawings, wherein:

Fig. 1 shows in crosssection a coaxial transmission line embodying aresistive terminator and operative in accordance with the principles ofthis invention; and

Fig. 2 is an exterior view of the assembly shown in Fig. 1.

As will be clear from the drawings the terminator consists of twoportions, and 11, separable at threaded junction 12.. Element 11consists of a nut portion soldered to a barrel portion 13, into which aresistive element 14, such as a one-half watt carbon resistor, isinserted. Axial mounting of resistor 14, as shown, will keep downreflection at higher frequencies because of symmetry of the capacitivedistribution over the dissipative path. Hollow conductive terminal pins15 and 16 are telescopically secured over the projecting ends (notshown) of the resistance wire component embodied in said resistor 14.

Another advantage of the design lies in the fact that a plurality ofelements, such as element 11, containing resistors of different valuesmay be kept on hand to rapidly vary the resistive component in order tovary the load with changes in operating frequency. Such variations inload are necessary to maintain the characteristics of an infinite line,thus producing a standing wave ratio of unity. Theoretically noreflections would be produced it the load could be accurately maintainedat the above stated conditions. 15 and 16 are maintained in an axialposition free from contact with the terminator shell by means of washers17 and 18. Washers 17 and 18 may be readily machined to a snugdiametrical fit from some suitable insulating material such as Teflon(tetrafluorethylene).

An additional function of washers 17 and 18 is to act as a bearing andtake up the end play between resistor 14 and the soldered' junction 19where conductor pin 15 meets the terminator shell, and between resistor14 and sleeve 20 when element 11 is screwed all the way into element 10.

A further function of washers 17 and 18 is to provide a dielectricmaterial to displace a substantial part of the air from the inside ofthe terminator unit. This would serve to prevent undesirable capacitanceeffects.

Sleeve 20 may be machined from the same material as washers 17 and 18and is turned inwardly at one end to serve as a guide and bearing forthe central conductor 21 of the coaxial transmission line or externalenergy source. It also brings conductor 21 into electrical contact withconductor pin 16 of resistor 14. Pin 16 in the embodiment illustrated inFig. 1 will act as a female receptacle to receive the solid probe 21.However, in some cases it may be desirable to reverse this male-femalearrangement. Attachment to a coaxial line or energizing source isfurther facilitated by means of spring 22 and female bayonet fitting 23,which may be designed to receive an appropriate male fitting 24 carryinglocking pins 23a properly secured to the conductor to be terminated. Inaddition to providing tension for the bayonet fitting, spring 22 assumesthe further function of maintaining good electrical contact at alljunctions by means of its action on the circumferential lip 24 ofelement 25 which in turn urges flange 26 of element 25 against theshoulder 27.

Although the invention has been described with reference to a particularembodiment it will be understood to those skilled in the art that theinvention is capable of a variety of alternative embodiments within thespirit and scope of the appended claims.

The invention claimed is:

1. A device for terminating a coaxial line comprising a sectionalmetallic housing, serving as an outer conductor, which is readilyseparable at a junction into a plurality of complementary sections, oneof said sections having smooth-bored cylindrical portions of large andsmall diameters, respectively, with the larger bore carrying acylindrical resistive element axially disposed therein, said resistorhaving axially aligned pins extending for a substantial distance beyondeach end thereof, one of said pins being in electrical contact with thesmaller bore of said metallic housing; and another of said separablesections carrying means to facilitate snap action coupling to anenergizing source together with means for bringing the second ofaforesaid resistor pins into electrical contact with said energizingsource, and dielectric means surrounding the first of said pins and,together with said resistive element, substantially filling said housingsection, to prevent undesirable capacitance effects.

2. A device as defined in claim 1 wherein said coupling means comprisesinterlocking inner and outer cylindrical elements, said outercylindrical element being circum: ferentially slotted and said innercylindrical element hav- Terminal pinsing means extending radiallytherefrom for retention in the slotted portion of said outer element.

3. A coaxial line termination comprising a tubular package, containingresistance wire, said package having hollow pins at the two ends thereofto clasp the projecting ends of the resistance wire, and means forlocking the end portion of an inner coaxial conductor within one of saidhollow pins, said means including a smoothbored metallic barrel fittingsnugly about said tubular resistance package, said barrel having athickened end portion fitting snugly about the other of said hollowpins, and electrically bonded thereto.

References Cited in the file of this patent UNITED STATES PATENTS VioletNov. 17, Eisenstein Nov. 2, Melcher May 15, Johnson Dec. 2, OcnaschekJan. 12, Bird Jan. 25, May Aug. 21, Rosenberg June 17, Federico Feb. 24,

